The disclosure relates generally to turbomachines, and more particularly, to a turbine airfoil having a near wall, trailing edge cooling circuit formed by a cover and allowing coolant recycling.
Gas turbine systems are one example of turbomachines widely utilized in fields such as power generation. A conventional gas turbine system includes a compressor section, a combustor section, and a turbine section. During operation of a gas turbine system, various components in the system, such as turbine blades and nozzle/vane airfoils, are subjected to high temperature flows, which can cause the components to fail. Since higher temperature flows generally result in increased performance, efficiency, and power output of a gas turbine system, it is advantageous to cool the components that are subjected to high temperature flows to allow the gas turbine system to operate at increased temperatures.
A multi-wall rotating blade or stationary nozzle typically contains an intricate maze of internal cooling passages. Cooling air provided by, for example, a compressor of a gas turbine system, may be passed through and out of the cooling passages to cool various portions of the multi all blade. Cooling circuits formed by one or more cooling passages in a multi-wall blade/nozzle may include, for example, internal near wall cooling circuits, internal central cooling circuits, tip cooling circuits, and cooling circuits adjacent the leading and trailing edges of the multi wall blade. In order to cool a tip of a trailing edge of a turbine airfoil and because the trailing edge provides very little internal space for defining a cooling circuit, coolant for the trailing edge is typically delivered in one or both of the following ways. In one approach, the airfoils include a coolant passage(s) that delivers a coolant through and out of the trailing edge, and in another approach, coolant is delivered out a side of the airfoil and across an exterior surface immediately upstream of the tip of the leading edge. In either approach, the coolant is delivered only in a single, downstream direction out to the hot gas path of the turbine. Once the coolant leaves the airfoil it is lost and cannot be recycled for cooling other parts.